Final answer:
A decrease in resource availability might have caused the outward movement of the production possibility frontier.
Step-by-step explanation:
An improvement in technology that reduces the cost of production will cause an increase in supply. This can be shown as a rightward (or downward) shift in the supply curve. A decrease in resource availability, on the other hand, will cause a decrease in supply or a leftward (or upward) shift in the supply curve. Therefore, option c) a decrease in resource availability might have caused the outward movement of the production possibility frontier.